In power transmission networks alternating current (AC) power is typically converted to direct current (DC) power for transmission via overhead lines and/or under-sea cables. This conversion removes the need to compensate for the AC capacitive load effects imposed by the transmission line or cable and reduces the cost per kilometer of the lines and/or cables, and thus becomes cost-effective when power needs to be transmitted over a long distance.
HVDC power converters are used to convert AC power to DC power. Semiconductor switching elements, such as thyristors, are a key component of HVDC power converters, and act as controlled rectifiers to convert AC power to DC power and vice versa.
While such semiconductor switching elements have very high breakdown voltages and are capable of carrying high current loads, even semiconductor switching elements from the same batch exhibit different performance characteristics. This creates difficulties in the operation of, e.g. a HVDC power converter in which the semiconductor switching elements are incorporated.